The violent man cannot become non-violent by any effort. Then is there no possibility? Yes, there is a possibility, but it is not through effort, not through will, not through practicing being other than you are. The possibility is by becoming aware.
Rather than trying to be non-violent, become aware of your violence, of how your violence functions.
See the roots of it. Go deep into it, into how it arises, into how it permeates your being and your activities. Watch violence, and in the very watching, becoming aware of it, you will be surprised: it starts disappearing.
Nobody can be consciously violent: this is a fundamental law, the secret. Nobody can be consciously violent; so all that is needed is to bring consciousness, to become more conscious, to become more meditative. Nobody can be meditatively angry; that is not possible.